Pathogenesis of primordial odontogenic tumour based on tumourigenesis and odontogenesis

Primordial odontogenic tumour (POT) is a rare benign mixed epithelial and mesenchymal odontogenic tumour. POT is composed of dental papilla-like tissue covered with cuboidal to columnar epithelium that resembles to inner and outer enamel epithelium of the enamel organ without dental hard tissue formation. The aim of this study was to examine pathogenesis of POT based on tumourigenesis and odontogenesis.

Six cases of POT were submitted for study. DNA analysis and transcriptome analysis were performed by next-generation sequencing. Expression of amelogenin, ameloblastin and dentin sialophosphoprotein (DSPP) was examined by immunohistochemistry.

There were no gene mutations detected in any of analysed 151 cancer- and 42 odontogenesis-associated genes. Enamel protein-coding genes of Amelx, Ambn and Enam, and dentin protein-coding genes of Col1a1, Dspp, Nes and Dmp1 were expressed, whereas expression of dentinogenesis-associated genes of Bglap, Ibsp and Nfic was negative or very weak suggesting inhibition of dentin formation in POT after odontoblast differentiation. Immunoreactivity of amelogenin, ameloblastin and DSPP was detected in POT.

Pathogenesis of POT is considered to be genetically different from other odontogenic tumours. It is suggested that inhibition of enamel and dentin formation in POT is due to defects in dentin formation process.